A. Field of the Invention
The present invention generally relates to measuring systems and, more particularly, to systems for determining an envelope, such as a clearance or maximum cargo envelope, about a path of travel, for example, a section of railroad tracks.
B. Description of the Prior Art
A need exists for railroads to determine the maximum cargo size that may be transported on a railroad car along a section of railroad track or along a specific railroad route. This need particularly exists when it is desired to transport an oversize load on a railroad car. The clearance or maximum cargo envelope about the railroad track over a particular section or along an entire route must be known before an oversize load can be shipped without fear of damage.
In the past, efficient, inexpensive and rapid systems have not been available for determining clearance or maximum cargon envelopes about sections of railroad tracks. Two prior art devices or systems are described in U.S. Pat. Nos. 3,168,023 (Harmon) and 3,705,772 (Andreas). The device described in the Harmon patent utilizes a high pressure arc lamp mounted on a railroad vehicle for projecting a plane of light radially along the path of travel of the vehicle. A photographic camera having a wide angle lens is utilized periodically to photograph and record on a photographic film medium the obstacles along the path of travel illuminated by the plane of light. The resulting photographs may then be viewed on a calibrated viewing screen to determine the clearance envelope at the point where each photograph was taken.
The device described in the Andreas patent utilizes a mobile computer controlled scanning system utilizing a light emitting diode and a rotating mirror to provide a radially directed rotating beam for illuminating objects along the path of travel. The computer controlled system collects the reflected light beam and ultimately generates binary data representative of the radial distances on a number of points along a preselected portion of each 360.degree. sweep of the beam. The data for each sweep is compared by the mobile computer with the data obtained from successive sweeps. Normally, only the data representing the smallest distance along any radial line is stored by the remote computer and periodically placed on a suitable output medium for further processing by a centrally located computer.
While these systems provide a way to determine clearance or maximum cargo envelopes about a path of travel, the photographic system requires each photograph to be individually viewed and the clearance envelope information provided by each photograph to be tabulated. Furthermore, obstacles located between the photographed areas will not be detected. These undetected obstacles can cause damage to a railroad cargo.
The computer controlled system provides a more convenient way of collecting and tabulating the results of the radial distance measurements; however, the system is relatively complex and requires the use of a mobile computer to control the system and to process the data. Such mobile computers are relatively expensive and are subject to damage by the shock and vibrations often encountered on a railroad vehicle. Furthermore, the computer controlled system only stores and outputs selected data, such as periodically determined minimum radial distance data, thereby limiting the flexibility of the system and precluding subsequent error checking of the data by comparing the results of successive scans.